diff --git a/src/AutoConnectDefs.h b/src/AutoConnectDefs.h
index dc35053..c59993b 100644
--- a/src/AutoConnectDefs.h
+++ b/src/AutoConnectDefs.h
@@ -135,6 +135,9 @@
 // SD pin assignment for AutoConnectFile
 #ifndef AUTOCONNECT_SD_CS
 #if defined(ARDUINO_ARCH_ESP8266)
+#ifndef SD_CHIP_SELECT_PIN
+#define SD_CHIP_SELECT_PIN      SS
+#endif
 #define AUTOCONNECT_SD_CS       SD_CHIP_SELECT_PIN
 #elif defined(ARDUINO_ARCH_ESP32)
 #define AUTOCONNECT_SD_CS       SS
@@ -143,11 +146,7 @@
 
 // SPI transfer speed for SD
 #ifndef AUTOCONNECT_SD_SPEED
-#if defined(ARDUINO_ARCH_ESP8266)
-#define AUTOCONNECT_SD_SPEED    SPI_HALF_SPEED
-#elif defined(ARDUINO_ARCH_ESP32)
 #define AUTOCONNECT_SD_SPEED    4000000
-#endif
 #endif // !AUTOCONNECT_SD_SPEED
 
 // ArduinoJson buffer size
diff --git a/src/AutoConnectUploadImpl.h b/src/AutoConnectUploadImpl.h
index baf935e..dc70fcd 100644
--- a/src/AutoConnectUploadImpl.h
+++ b/src/AutoConnectUploadImpl.h
@@ -102,6 +102,15 @@ class AutoConnectUploadFS : public AutoConnectUploadHandler {
   SPIFileT  _file; 
 };
 
+// Fix to be compatibility with backward for ESP8266 core 2.5.1 or later
+#ifdef ARDUINO_ARCH_ESP8266
+#if defined(SD_SCK_HZ)
+#define AC_SD_SPEED(s)  SD_SCK_HZ(s)
+#else
+#define AC_SD_SPPED(s)  s
+#endif
+#endif
+
 // Default handler for uploading to the standard SD class embedded in the core.
 class AutoConnectUploadSD : public AutoConnectUploadHandler {
  public:
@@ -111,7 +120,7 @@ class AutoConnectUploadSD : public AutoConnectUploadHandler {
  protected:
   bool  _open(const char* filename, const char* mode) override {
 #if defined(ARDUINO_ARCH_ESP8266)
-    if (_media->begin(_cs, _speed)) {
+    if (_media->begin(_cs, AC_SD_SPEED(_speed))) {
       uint8_t oflag = *mode == 'w' ? FILE_WRITE : FILE_READ;
 #elif defined(ARDUINO_ARCH_ESP32)
     if (_media->begin(_cs, SPI, _speed)) {